The invention relates generally to vacuum assisted rolls, and more particularly to a vacuum timing device that compensates for the delay in vacuum propagation along the length of the roll.
It is well known to utilize vacuum means to transfer webs from roll to roll or from a roll to another device such as a set of guide rods. The vacuum is selectively applied through apertures at selected circumferential locations on the rotating roll in order to hold a web of material to the roll for a desired time or along a desired path. As used herein and in the appended claims, the term xe2x80x9cwebxe2x80x9d means any material (including without limitation paper, metal, plastic, rubber or synthetic material, fabric, etc.) which can be or is found in sheet form (including without limitation tissue, paper toweling, napkins, foils, wrapping paper, food wrap, woven and non-woven cloth or textiles, etc.). The term xe2x80x9cwebxe2x80x9d does not indicate or imply any particular shape, size, length, width, or thickness of the material.
FIG. 1 illustrates a typical prior art vacuum roll system 10 for use in operations requiring web transfer. The prior art vacuum roll system 10 includes a roll 14 having an axis of rotation 18 and a surface 22. The surface 22 has a plurality of apertures 26 therein which are spaced longitudinally along the length of the roll 14 forming a straight row 30. Typically, there are a plurality of straight rows 30 (e.g., four rows spaced at ninety-degree angles), around the surface 22. Each row 30 is in fluid communication with a vacuum line 34. Normally, the vacuum line 34 is a bore that extends longitudinally along the length of the roll 14 just beneath the surface 22. The apertures 26 are typically drilled through to the vacuum line 34, thus providing the fluid communication between the apertures 26 and the line 34. The line 34 has an vacuum inlet 38 in at least one end of the roll 14, the purpose of which will be described below.
In prior art devices, a rotary vacuum valve 42 is usually coaxially coupled to the roll 14 at one end and is fixed against rotation. The valve 42 is connected to a vacuum source (not shown) at a valve inlet 50. The valve 42 also includes an arcuate groove 54 in the end adjacent the roll 14. The arcuate groove 54 is in fluid communication with the valve inlet 50. The arcuate groove 54 is spaced radially from the axis of rotation 18 such that it can be in fluid communication with the line 34. In operation, the vacuum source creates a vacuum that enters the valve 42 at the valve inlet 50. As the roll 14 rotates to angular position A, the vacuum inlet 38 of the line 34 is adjacent the arcuate groove 54. The vacuum therefore enters the vacuum inlet 38 and propagates longitudinally along the length of the line 34. As the vacuum propagates, the apertures 26 experience the vacuum which is then applied to the web, holding the web to the surface 22 of the roll 14. As the roll 14 rotates to angular position B, the fluid communication between the vacuum inlet 38 and the arcuate groove 54 is blocked, thereby cutting off the vacuum supply to the line 34 and apertures 26. The line 34 is often vented in a conventional manner to remove the vacuum inside the line 34 quickly. By changing the length of arcuate groove 54, the timing of vacuum application and removal can be modified to suit a specific application. The description of the prior art vacuum valve 42 is only presented by way of illustration. Other types of vacuum valves (not shown) are also commonly used in prior art vacuum roll systems 10.
Surface speeds of the roll 14 typically vary depending upon application, but can reach 600 feet per minute or higher. Vacuum propagates through each line 34 at the speed of sound. Therefore, for long rolls 14 rotating at such high speeds, it is common to encounter angular delay in the propagation of the vacuum along the lines 34. For example, when roll 14 reaches angular position A, and the vacuum is introduced into the vacuum inlet 38, it is common in longer rolls 14 for the vacuum to reach the apertures 26 closest to the vacuum inlet 38 almost instantaneously while reaching the apertures 26 located farthest from the vacuum inlet 38 at a measurably later time. Often, the vacuum will not reach the apertures 26 located farthest from the vacuum inlet 38 until the roll has rotated to an angular position A+xcex94A. When this angular delay occurs, the portion of the web (not shown) closest to the vacuum inlet 38 will experience the vacuum before the portion of the web farthest from the vacuum inlet 38. This can cause binding, inadequate web retention, or misalignment of the web, resulting in flawed product, jams, misfeeds, wrinkling and/or even line shut-down.
Angular delay will also be experienced when vacuum is removed from the lines 34. For example, when roll 14 reaches angular position B, and the communication between the vacuum inlet 38 and the arcuate groove 54 is blocked, it is common in longer rolls 14 for the vacuum to remain in the apertures 26 located farthest from the inlet opening longer than the vacuum remains in the apertures 26 located nearest to the vacuum inlet 38. Thus, the vacuum will not be removed from the apertures 26 located farthest from the vacuum inlet 38 until the roll has rotated to an angular position B+xcex94B. When this occurs, the portion of the web closest to the vacuum inlet 38 will be released from the surface 22 earlier than the portion of the web farthest from the vacuum inlet 38. Again, this can cause the above-mentioned problems. FIG. 2 shows an exaggerated profile of the angular delay just described. The profile illustrates the angular location of the apertures at the actual point of vacuum removal.
Attempts to alleviate the problem of angular delay have led to the use of two rotary vacuum valves 42, one on each end of roll 14. Each valve 42 has its own valve inlet 50 and arcuate groove 54. Each arcuate groove 54 communicates with an adjacent vacuum inlet 38 at either end of the line 34. This configuration has reduced angular delay problems associated with long rolls 14 in that the vacuum need only propagate half the length of the roll 14. However, the high rotational speed demanded in many applications still results in angular delay near the center of the roll 14. Furthermore, the use of two vacuum valves 42 adds more parts to the vacuum roll assembly 10 which increases the cost, complexity and maintenance required of the system.
In light of the problems and limitations of the prior art described above, a need exists for a vacuum timing device that can account and compensate for angular delay of vacuum in a rotating vacuum roll, can perform such compensation at a variety of roll rotational speeds, presents a simple and inexpensive solution to the angular delay problems described above and permits the use of a vacuum roll at high speeds without the angular delay experienced in prior art vacuum rolls. Each preferred embodiment of the present invention achieves one or more of these results.
The invention provides a vacuum timing device for applying a vacuum on a roll. The vacuum timing device includes a roll with an axis of rotation, a surface, and a surface longitudinal axis that is oriented in a direction substantially parallel to the axis of rotation. The device also includes at least one vacuum inlet communicating with at least one vacuum line running along at least a portion of the length of the roll. The device also includes a plurality of apertures defined in a surface of the roll and in fluid communication with the vacuum line. In order to alleviate angular delay of vacuum propagation, the plurality of apertures is arranged in a line that is skewed with respect to the surface longitudinal axis. Preferably, the plurality of apertures is arranged in a line that is skewed away from the direction of rotation of the roll, thereby substantially eliminating the angular propagation delay as the vacuum roll operates.
For longer rolls, the device can include two or more pluralities of apertures, each being in fluid communication with a respective vacuum line. Using two pluralities of apertures reduces the vacuum propagation distance, thereby reducing the propagation delay. When these long rolls operate at high speeds, however, delay often still exists. Therefore, each plurality of apertures is arranged in a line that is skewed with respect to the surface longitudinal axis to compensate for the remaining angular delay.
The pluralities of apertures can be formed directly in the surface of the roll, or alternatively, can be formed in one or more vacuum members that are coupled to the roll. Rolls having the apertures formed directly in the surface are preferable when the roll will rotate in the same direction and with substantially the same rotational speed over its lifetime. Once the direction of rotation and the rotational speed are known, the plurality of apertures can be machined directly into the surface with the appropriate skew. In the event the production line is changed and the direction or speed of rotation is modified, a different roll having a different skew configuration could be substituted, or portions of a roll could be replaced.
On the other hand, rolls that incorporate at least one vacuum member provide greater flexibility in that the vacuum member is preferably movable. The vacuum member can be selectively positioned to accommodate the direction of roll rotation and any number of rotational speeds. Most preferably, the vacuum member can be selectively positioned to accommodate both possible directions of roll rotation. The vacuum member can be moved with respect to the surface longitudinal axis either manually or automatically in any suitable manner. Preferably, the vacuum member is pivoted either about its end or a center portion of the vacuum member. When the vacuum member is moved automatically via a suitable actuating device, it is preferable to electronically (via computer or electronic switching controls) or mechanically link the actuating device to the roll to allow for automatic adjustment of the vacuum member proportional to the rotational speed of the roll. When more than one vacuum member is used, the vacuum members preferably operate in substantially the same manner.
When a vacuum member is used, the preferred configuration includes a roll having a longitudinal gap in the surface. The gap receives and accommodates at least a portion of the vacuum member. The plurality of apertures are preferably formed in a central portion of the vacuum member and communicate with the vacuum line in the roll. Preferably, the vacuum member also includes tab portions that extend from either side of the central portion. The tab portions are preferably received in respective grooves that are located radially in the roll. Preferably, the location of the grooves is such that when the vacuum member is inserted, the plurality of apertures in the central portion are at substantially the same radial distance from the axis of rotation as the surface. Alternatively, the location of the groove can be varied so that the plurality of apertures is slightly recessed or raised from the surface of the roll.
The grooves and gap are preferably appropriately sized to permit movement of the vacuum member relative to the roll. The vacuum member is preferably made from a flexible material so that as the vacuum member is pivoted it wraps partially around the roll, thereby skewing the plurality of apertures with respect to the surface longitudinal axis. The vacuum line should be large enough to accommodate preferably the entire range of movement available to the plurality of apertures. When more than one vacuum member is used, the vacuum members are preferably configured in substantially the same manner.
More information and a better understanding of the present invention can be achieved by reference to the following drawings and detailed description.